This invention relates to an aqueous coating compound based on binders containing polyurethane resin and to their preparation. The coating compounds are suitable for the production of weather-resistant coats, in particular top lacquer coats. They may be used, for example, for multilayered lacquering, in particular in the field of motor vehicles.
The use of a polyurethane dispersion chain lengthened with polyamine for the preparation of hydrobase coats in combination with a clear lacquer is described in EP-A 0 089 497. According to DE-A-26 28 124 or DE-A-40 00 889, for example, good properties can be obtained by using such resins. These lacquerings, however, still leave room for improvement as regards the metallic effect and the weather resistance (sweat box test).
Water dilutable base coats are prepared according to DE-A-39 15 458 and EP-A-0 379 158 from combinations of acrylate resins and polyurethane dispersions which undergo uncontrollable chain lengthening when dispersed in water. In these products, solution polymers provide insufficient solvent resistance and adherence under repair conditions (30-60 min at 80.degree.-90.degree. C.) while emulsion polymers provide insufficient sweat box resistance (weather resistance) due to their emulsifiers, especially under drying conditions at low temperatures.